Mechanical and chemical-mechanical planarization processes (collectively “CMP”) remove material from the surfaces of microfeature workpieces in the production of microelectronic devices and other products. Typically the microfeature workpieces then undergo a post-CMP cleaning process. For example, FIG. 1 schematically illustrates a brushing machine 50 in accordance with the prior art used for this purpose. Such devices are available from Applied Materials of Santa Clara, Calif. The brushing machine 50 supports a microfeature workpiece 10 on rollers 20. The rollers 20 engage an edge surface 11 of the microfeature workpiece 10 and rotate as indicated by arrows A to rotate the microfeature workpiece 10 as indicated by arrow B. As the microfeature workpiece 10 rotates, it engages two rotating brushes 30. The rotating brushes 30 rotate in opposite directions to remove particles from opposing faces 12 of the microfeature workpiece 10. Optionally, the microfeature workpiece 10 can be exposed to a chemical compound while it is brushed.
One drawback with the foregoing arrangement is that the microfeature workpiece 10 occasionally stops rotating during the brushing process. As a result, the microfeature workpiece 10 may be incompletely cleaned, and may also be damaged as the rotating brushes bear against a limited portion of the microfeature workpiece 10. Furthermore, because the microfeature workpiece 10 typically rotates at high speed (e.g., about 500 rpm), it is often hard for an operator to determine that the microfeature workpiece 10 has stopped rotating.
One approach to addressing the foregoing drawback is to engage a follower wheel 40 with the edge surface 11 of the microfeature workpiece 10. The rotation of the microfeature workpiece 10 causes the follower wheel 40 to rotate. A sensor (not shown) detects whether or not the follower wheel 40 is rotating. If the follower wheel 40 ceases to rotate, the operator assumes that the microfeature workpiece 10 is no longer rotating and can remove the microfeature workpiece 10 or re-engage it with the rollers 20.
One drawback with the follower wheel 40 is that it may not be reliable. For example, the follower wheel 40 can wear out, fall out of adjustment, seize, slip, or fail in other manners that can result in a false indication of the motion (or lack of motion) of the microfeature workpiece 10. Accordingly, an operator may be unaware that the microfeature workpiece 10 has stopped rotating, or may receive false warnings that the microfeature workpiece 10 has stopped rotating.